Metal smelting processes are normally carried out with an auxiliary burner that utilizes air, oxygen enriched air or technically pure oxygen as the oxidant. Technically pure oxygen or oxygen enriched air is typically employed as the oxidant in order to improve the smelting rate of the metal bearing materials. The use of technically pure oxygen or oxygen enriched air, however, produces significantly increased peak flame temperature over that produced by using air as the oxidant. This high peak flame temperature kinetically favors the formation of nitrogen oxides.
During metal smelting operation, sulfur is released from metal bearing materials. Sulfur is then combusted to form sulfur dioxides. Thus, the gas resulting from the smelting operation contains sulfur dioxides. This gas is normally contaminated with a small amount of nitrogen oxides due to nitrogen oxides which is formed during combustion of sulfur and fuel with oxidant. The amount of nitrogen oxides contamination is increased with the increased generation of nitrogen oxides. As a result of the presence of nitrogen oxide in the gas, the sulfur dioxides therein is also contaminated with nitrogen oxides. Since the contaminated sulfur dioxides is often used to produce by-product sulfuric acid, the purity of the by-product sulfuric acid is lowered. This low quality sulfuric acid is often commercially undesirable because nitrogen oxides impurities may interfere with the end use of the resulting sulfuric acid and may cause corrosion problems.
Accordingly, it is an object of the invention to provide a method for combusting sulfur with reduced contamination of the resulting gaseous product with nitrogen oxides.
It is another object of the invention to provide a smelting gas which is useful for producing high quality sulfuric acid.
It is yet another object of the invention to utilize technically pure oxygen or an oxygen enriched air as the oxidant to improve the smelting rate of metal bearing materials and, at the same time, combust sulfur vapor released from the metal bearing materials to form sulfur dioxides with reduced contamination of sulfur dioxides with nitrogen oxides.